An apparatus for extrusion of a thermoplastic material can comprise an extruder with an extruder screw and an extruder housing with a feed opening, a feed device, an extrusion die, a drive for the extruder screw with a variable speed motor and a regulating or control cascade or array for the mass temperature.
The regulating cascade has a plurality of tempering zones, at least one mass temperature detector and at least one tempering temperature-control unit downstream of the feed opening and upstream of the extrusion die.
One tempering zone connected directly to the feed opening is part of the regulating cascade and the temperature in that one temperature control zone is corrected to a set-point value upon a mass temperature variation. Further, the drive speed of the variable speed motor is reduced in the event of an excessive throughput and vice versa. The mass temperature can be measured directly by a temperature detector or indirectly, e.g. by the viscosity.
A regulating device cascade in an apparatus for extrusion of thermoplastic material is known. By "regulating device cascade" I mean a series or group of regulating devices which control the mass temperature using the wall temperature of the extruder housing as an auxiliary value with a corresponding auxiliary regulating loop.
In the temperature control zones a heating or cooling occurs according to the design of the controlling assembly. Usually five or six temperature control zones are provided along the length of the extruder housing.
In the known apparatus on which my invention is based (H. G. Wiegand, "Proze.beta.automatisierung beim Extrudieren and Spritzgie.beta.en von Kunststoffen", Munich/Vienna, 1979, Page 37, 38; the journal "Plastvorarbeiter(PV)", Vol. 24, 1973, page 598 to 602) the temperature control portion of the extruder connected to the feed opening comprises a heating device and is provided with a smooth passage in which the extruder screw operates.
The regulating cascade affords a rapid control of the variations in the individual temperature control zones by the auxiliary control loop, and in regard to the mass temperature, a high control reliability.
As has been shown in practice independently of the variation size and the operating level of the extruder dependable control of the mass temperature is guaranteed over a regulating range of +/-50.degree. C.
The regulating cascade is subject to external control if, because of prior events and resulting measured values, the difference between the mass temperature actual value and the preset set value becomes larger. ("Plastverarbeiter(PV)", l.c., Page 600, right Column, lines 7 to 14). Among other things in this known apparatus the feed of material delivered to this region which connects to the feed opening, the so-called entrance region, is in need of improvement.
To improve the feed of material delivered to the entrance of an extruder it is known to provide a cooled grooved sleeve in the region of the entrance or feed opening. ("Plastverarbeiter (PV)", Vol. 23, 1972, Page 332, FIG. 1). A grooved sleeve at the entrance, of course, stabilizes the feed of the delivered material. However, the existing regulation range is reduced to +/-10.degree. C. which impairs the entire availability of the apparatus in regard to the preparation of various thermoplastic materials.